1. Field of the Invention
This invention relates to an improved hollow shaft filament trimmer for use in safely cutting vegetation.
2. Description of the Prior Art
Filament-type vegetation trimmers are well known in the art. With such apparatus, a length of stiff filament line is rapidly slung in a circular arc to provide cutting means which are relatively safe to use in comparison with bladed trimming mechanisms.
The better models of said trimmers normally use a frame mounted rotary drive means having a hollow output shaft. A length of filament line is fed through the hollow shaft to a rotating head mounted on said shaft which engages the line and slings it in a radial plane to the shaft axis. As the cutting line wears or breaks, additional line is fed through the hollow shaft to the rotating head from a reserve supply of filament mounted above the rotary drive means. As the centrifugal force of the moving line will pull the line from the reserve filament, the filament trimmers have a filament lock interposed between the reserve supply and the hollow shaft which may be released to allow additional line to descend through the hollow shaft to the rotating head.
The hollow shaft feed filament trimmer disclosed in U.S. Pat. Application No. 3,928,911 is illustrative of such a trimmer. In the aforementioned invention, the rotating head mounted to the hollow shaft comprises an open-ended bellmouth structure having one or more radial grooves for engaging and swinging the filament in a plane perpendicular to the hollow shaft. A pair of spring biased toothed jaws grip the filament line above the hollow shaft, and a manual control mechanism is used to open the jaws during operation for feed of additional line to the bellmouth through the hollow shaft.
The aforementioned device and similar type trimmers have certain disadvantages incorporated therein which become apparent upon observation. One problem lies in initially getting the filament line to swing in the radial plane. Admittedly, once the filament is started swinging, centrifugal force might keep the line pressed in the radial groove of the open bellmouth, however, there is nothing disclosed to initiate such an action. In addition, the rotation of the head forces the filament to turn in the bellmouth groove which tends to roll the filament from the groove. Furthermore, if the filament is swinging rapidly, the centrifugal force on the line makes the addition of fresh filament a matter of guesswork and there are no convenient means to retrieve excess filament once an error has been made.
It is therefore an object of this invention to provide an improved hollow shaft filament trimmer having a novel rotating head and positive filament control means which overcome the problems associated with the prior art.